Well, one can deduce the rough height of Melkor and his servants through logic reasoning
. It's safe to assume that Melkor would've been the tallest, being the Dark Lord and all that. Knowing Melkor's personality we can conclude that he would not allow one of his servants to be taller than himself. We also know that Glorfindel fought a Balrog and stabbed him in the stomach or chest and we know that the Balrog of Moria was small enough to attempt to enter the Chamber of Mazarbul so it's obvious that the movie Balrog is too large. My personal estimate is that the average Balrog was probably around 3 meters tall, still enough to tower over any of the Children of Iluvatar. Melkor himself would be even bigger, probably approaching 4 meters. Anything taller that 4 meters and the whole duel between him and Fingolfin will start to take on comedic qualities, with Fingolfin hacking away at Melkor's toes. At 4 meters Melkor would've been twice as tall as Fingolfin, more than enough to stand 'before the King like a tower, iron-crowned, and his vast shield, sable enblazoned, cast a shadow over him like a stormcloud.' Fingolfin would've been able to hit most of Melkors body with his sword, taking the reach of his blade into account. It also means that Melkor's foot is small enough to 'set his left foot upon his neck, and the weight of it was like a fallen hill.' If Morgoth was as tall as some artists depict him than 'And Morgoth set his left foot upon his neck, face and entire upper body and the weight of it was like a fallen hill.' would've been a more accurate desciption of the event.
